The present invention relates to a rock drilling tool for percussive drilling comprising a drill bit and a drill tube. The drill bit has a head having a front surface wherefrom a number of front inserts are project and peripheral inserts provided in a peripheral row. The drill bit is provided with a first thread co-operating with a second thread provided on the drill tube. The invention further relates to a drill bit and a method of transferring percussive energy from a rock drilling tool to a bore hole.
It is previously known through U.S. Pat. No. 1,447,855 to provide a so called shoulder abutment at threaded connections between a drill rod and a rock drill bit in equipment for percussive drilling. When loosening the drill bit in the known equipment with a relatively heavy drill bit, there is a risk that the thread entrance on the bit shank will become damaged due to the substantial difference in mass on opposite sides of the shoulder abutment. Furthermore, the known drill bit is provided with chisel edges of hardened steel, which project relatively far in the radial direction. This means that the percussive energy during percussive drilling is forced to deflect towards the radially outer tip of the edge and therefore the effective coefficient of efficiency decreases, thereby resulting in impaired guiding ability and impaired drilling speed. Chisel edges give a relatively slow drilling speed. Furthermore it seems as the known tool can have abutment between the drill rod and bit, both in the radial and axial directions which during drilling create hardening of the material with subsequent crack initiation points.